This invention relates to a process for the carbonylation of ethylenically unsaturated compounds by reaction with carbon monoxide and a co-reactant in the presence of a palladium-containing catalyst system.
EP-A-495547 describes reactions in which optionally substituted olefinically unsaturated compounds are reacted with carbon monoxide and a co-reactant in the presence of a catalyst system comprising a source of palladium-cations, a source of specific aliphatic bidentate diphosphines and a source of anions. A variety of products are also described in the patent. These products are produced in accordance with disclosed carbonylation reactions depending upon the reactants, the prevailing reaction conditions and the selected catalyst system. The relative amounts of co-reactants, the composition of the diphosphine ligand and on the source of anions also greatly enhances or suppresses the production of these varying products.
For example, when an olefin is reacted with carbon monoxide and with an alcohol as co-reactant, the reaction product will be an ester. If an acid is selected as co-reactant, the reaction product will comprise an anhydride group. With ammonia, or a primary or secondary amine as co-reactant, an amide group-containing product will be obtained. The use of water as co-reactant will result in the formation of a carboxylic acid, while polarizable molecular hydrogen will react to form aldehydes and/or alcohols.
The catalyst system in that patent uses an aliphatic diphosphine ligand, Q.sub.1 Q.sub.2 PXPQ.sub.3 Q.sub.4), the groups Q.sub.1, Q.sub.2, Q.sub.3, and Q.sub.4, or one or both pairs of Q.sub.1 and Q.sub.2, and Q.sub.3 and Q.sub.4, preferably are unsubstituted, optionally branched or cyclic alkyl or alkylene groups having from 1 to 10 carbon atoms. These catalyst systems comprise, in addition to palladium cations and a diphosphine ligand, a source of anions. As anion source, Protonic acid are the preferred anion sources. Most notable among these acids are those which are sources of non-coordinating or weakly-coordinating anions, i.e. anions which do not or only weakly coordinate with the palladium cation. Thus, a particularly preferred source of anions is a strong acid having a pKa of less than 3.5. If the anions are derived from a weak acid, e.g. a carboxylic acid, the carboxylic acid is preferably sterically hindered. Bulky substituents on these weak acids will minimize the tendency for coordination.
While one skilled in the art can generally obtain desired products in reasonably good yields based on the teachings of EP-A-495547, reaction rates have been found to be disappointingly low. Of course, this greatly effects the commercial viability of these reactions. Accordingly, improving the reaction rates of carbonylation reactions without impeding such factors as selectivity and catalyst stability continues to be a highly sought goal.